Geochemistry, Zircon U-Pb Ages and Geological Significance of the Liushugou Formation Rhyolite in the Sepikou Region, Eastern Bogda, Xinjiang
详细信息
- 责任者：Gao Jinggang (Key laboratory of Western Chinas Mineral Resources and Geological Engineering ; Ministry of Education ; Science and Resources College ; Chang’an University ; Xi’an 710054 ; China) ; Li Wenyuan
- 刊名：Geology and Prospecting
- 出版年：2013
- 卷期：49(4)
- 关键词：流纹岩 ; rhyolites ; 岩石地球化学 ; lithogeochemistry ; 铀—铅计时 ; U-Pb dating ; 新疆 ; Xinjiang
- 页码：p.665-675
- 图表：illus., 3 tables, 31 refs.
- 分类号：0801
- issnNo：ISSN0495-5331
- isbnNo：CN11-2043/P
摘要
The Sepikou area in Xinjiang is located in the north of the eastern section of the Bogda orogenic belt, where the upper Carboniferous Liushugou Formation rhyolites are widely present. The rhyolites in the Sepikou area have SiO2 content between 70.81% and 77.62%; Na2O+K2O content between 6.87% and 9.02%; high K2O/TiO2 and K2O/P2O5 ratios(values are10.38~18.83 and 72.45~242.14, respectively), A/CNK ratios ranging between 1.43 and 1.55, with high-Al and high-Si characteristics. The rhyolites are characterized by high content of K, Rb, Th, Ba, and HFSE (Nb, Ta, Zr, Hf). ∑REE contents vary between 141.76×10-6 and 228.2×10-6 , with (La/Yb)N 4.11~7.42. They also display fractionated REE patterns with prominent negative Eu anomalies (δEu=0.27~0.50). Compared with the primitive mantle, the rhyolites are depleted of Sr, Nb, Ta, P and Ti,suggesting that they have experienced strong crystallization differentiation of magma. Zircon U-Pb ages of the rhyolite are 314.0±1.1Ma(n=17,MSWD=1.6, Th/U =0.39~0.80), representing the crystallizing age of the rhyolite. By comprehensive analysis of previous Sr, Nd, O and Hf isotopes, the Late Carboniferous rhyolite formed in the partial melting of basic igneous rock from depleted mantle, or fractional crystallization of basaltic magma by crustal material contamination and the partial melting of crust. It probably represents the product of the frequent conversion from extension to compression in the rift closing period.
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